What are the different grades of silicon metals

What is silicon metal

Silicon metal is a semiconducting metal with a grayish luster, also known as crystalline silicon or industrial silicon, which is mainly used as an additive in non-ferrous metal alloys. Its production is accomplished through a reduction reaction between quartz sand and coke in an electric furnace (chemical formula: SiO₂ + 2C → Si + 2CO), with a conventional purity of about 98% and a high purity of more than 99.99%.

Silicon metal grades are mainly based on the content of iron, aluminum, calcium and other impurities, and common grades include 553, 441, 411, 3303, 2202 and 1101. Understanding the differences between these grades is the key to industrial material selection.

Classification of Silicon Metal

Classification Core: Purity and Impurity Content

Silicon metal grades are classified based on the silicon content and the upper limit of impurities (iron, aluminum and calcium). In the production process, the initial 97-98% purity of silicon metal is produced by electric furnace reduction, and after melt recrystallization and acid treatment, the purity can be increased to 99.7-99.8%.

Silicon metal is often named with a combination of numbers (e.g., 553, 441), each of which corresponds to a decile percentage of impurity content.

What are the main grades of silicon metal

Low-grade silicon metal (97-98% silicon content)

97-grade silicon metal (industrial grade)

Silicon content ≥ 97%, with high impurity content. Because of its low cost, it is mainly used in steel deoxidation, low-end cast iron production, or as raw material for silicon carbide. In aluminum ingot smelting, 97 grade silicon improves alloy flow and casting performance.

Industrial / Metallurgical Grade Silicon Metal (98-99.5% Silicon Content)

553 Grade Silicon Metal

Silicon content ≥98.5%, iron, aluminum ≤0.5%, calcium ≤0.3%. Widely used in the manufacture of aluminum-silicon alloys, which can improve the corrosion resistance and casting performance of the alloy, and is also commonly used in the modification of cast iron and deoxidation of steelmaking.

441 Grade Silicon Metal

Silicon content ≥99.0%, iron, aluminum ≤0.4%, calcium ≤0.1%. It is suitable for the production of high-quality aluminum alloy and silicone chemicals (such as silicone oil and silicone resin), and is an important raw material in the chemical industry.

411 Grade Silicon Metal

Silicon content ≥99.4%, iron ≤0.4%, aluminum, calcium ≤0.1%. Because of its low aluminum and calcium content, it is commonly used in precision aluminum alloy casting and semiconductor intermediate material preparation to meet higher purity requirements of industrial scenarios.

Premium Industrial Grade Silicon Metal (99.3-99.5% silicon content)

3303 Grade Silicon Metal

Silicon content of 99.37% or more, iron, aluminum ≤ 0.3%, calcium ≤ 0.03%. It belongs to the higher grade of silicon metal and is suitable for the smelting of special steel, high-performance aluminum alloy (e.g. aerospace parts) and the production of silicone rubber, and can be used to further prepare silicon products with higher requirements through the purification process.

2202 Grade Silicon Metal

Silicon content ≥99.5%, iron, aluminum ≤0.2%, calcium ≤0.02%. Mainly used in aerospace materials, high-end silicone products, to meet the needs of industries that are extremely sensitive to impurities.

Ultra-high purity silicon metal (99.999% or more)

Solar Grade Silicon (SoG-Si)

Purity up to 5N (99.999%), total impurities < 100ppm, is the core raw material for photovoltaic cell wafers, and the cost is lower than semiconductor-grade silicon.

Electronic Grade Silicon (EG-Si)

Purity 6N-7N (99.9999%-99.99999%), impurities < 10ppm, used in the manufacture of semiconductor wafers, integrated circuits and other microelectronic components, is the basic material for the chip industry.

What is the use of different grades of silicon metal

Metallurgy

Aluminum-silicon alloys: 553- and 441-grade silicon is used in automotive and aerospace parts to reduce alloy density and improve resistance to wear and tear;

Silicon steel sheets: Adding silicon (e.g., 3303-grade) to steel enhances the magnetic permeability and reduces the energy loss in transformers and motors.

Electronics & Semiconductors

Electronic-grade silicon (EG-Si) is a core material for chip manufacturing, supporting high-end fields such as computers and communications equipment;

Solar-grade silicon (SoG-Si) promotes the development of the photovoltaic industry and aids in the transition to clean energy.

Chemical & Materials

3303, 2202 grade silicon is used to synthesize silicone (silicone oil, silicone rubber), and the products are widely used in high-temperature seals, waterproof coatings, etc.;

Preparation of heat-resistant materials (e.g., Si₃N₄), used in wear-resistant, corrosion-resistant industrial components.

Factors Affecting Grade Selection

Application Requirements

Semiconductor manufacturing requires electronic-grade silicon (EG-Si), while steelmaking requires only metallurgical-grade silicon (e.g., Grade 97);

Aluminum casting, where iron content needs to be controlled to prevent the alloy from becoming brittle, requires grade 441 or higher.

Cost and Performance

The price of high purity silicon (e.g. 2202 grade) is much higher than that of industrial grade (e.g. 553 grade), so it is necessary to choose according to the actual performance requirements, and to avoid excessive pursuit of purity to increase costs.

Process compatibility

Different smelting processes have different sensitivities to impurities in silicon, for example, precision casting requires strict control of calcium content, and 3303 grade is preferred to 553 grade.

Conclusion

The classification of silicon metal is a typical expression of “material selection according to demand” in the industrial field. With the development of semiconductor, new energy and other industries, the demand for high-purity silicon metal will continue to grow, and reasonable selection of grades, optimize the cost and performance, is still the key to enhance the competitiveness of various industries.